Plugins: Pass build mode to frontend (#114092)

* pass build mode to frontend

* set buildMode build time using shared plugin webpack conf

pkg/plugins/plugins.go

@@ -133,6 +133,9 @@ type JSONData struct {
 
 	// List of languages supported by the plugin
 	Languages []string `json:"languages,omitempty"`
+
+	// Build mode of the plugin (set automatically at build time)
+	BuildMode string `json:"buildMode,omitempty"`
 }
 
 func ReadPluginJSON(reader io.Reader) (JSONData, error) {